The present invention generally relates to a light source unit and an optical scanning image recording apparatus, and more particularly to a light source unit capable of changing the size of a light beam spot, and an optical scanning recording apparatus using the same, used in laser printers and the like.
Recently, an optical scanning recording apparatus has been developed. In this optical scanning recording apparatus, a laser beam modulated in accordance with information supplied from a computer, a word processor or the like scans an image forming medium such as a photosensitive member so that a latent image is formed on the surface of the image forming medium. Then, a dot image based on the latent image formed on the image forming medium is formed on a recording sheet.
In this type of optical scanning recording apparatus, various methods of controlling a dot size which is the size of a laser beam spot projecting onto the image forming medium have been proposed in order to obtain a half-tone image. For example, Japanese Laid-Open Patent Application No. 61-113018 discloses an optical scanning recording apparatus in which the size of a laser beam spot is controlled by use of a flare stop. That is, the size of the flare stop is controlled by a controller so that the size of the laser beam spot projecting onto the image forming medium is changed. In addition, Japanese Laid-Open Patent Application No. 63-296069 discloses an optical scanning recording apparatus in which the intensity of the laser beam is controlled so that the size of the laser beam spot projecting onto the image forming medium is changed. In this apparatus, when image information of two adjacent dots corresponds to a case where the laser beam does not project onto the image forming medium, the dot size is enlarged so as to prevent a line image from being separated.
In the optical scanning recording apparatus disclosed in Japanese Laid-Open Patent Application No. 61-113018, a mechanical flare stop, a liquid crystal flare stop or the like is used as the flare stop. The response of each of the above types of flare stops is slow so that it is difficult to rapidly record the half-tone image.
In the optical scanning recording apparatus disclosed in Japanese Laid-Open Patent Application No. 63-296069, the intensity of the laser beam is changed s that it is difficult to sufficiently change the dot size of the image formed on the image forming medium.